1. Field of the Invention
The present invention relates to a luminescent light emitting device having a luminescent material plate that is caused to be luminous by an excitation light source and a projector including the same luminescent light emitting device.
2. Description of the Related Art
In these days, data projectors are used on many occasions as an image projection system which projects images including an image of a screen or a video image of a personal computer, as well as images based on image data which is stored on a memory card on to a screen. Conventionally, the mainstream of these projectors has been those which utilize a high-intensity discharge lamp as a light source. In recent years, however, there have been made many developments and proposals on light source devices which use, as a light emitting element of a light source, a light emitting diode (LED) or a laser oscillator, an organic EL device, a luminescent material or the like.
For example, Japanese Unexamined Patent Publication No. 2004-341105 proposes a light source device in which a red luminescent material layer, a green luminescent material layer and a blue luminescent material layer are provided in an end-to-end fashion on a surface of a color wheel that is made up of a light transmitting circular disc, a dichroic filter that transmits ultraviolet radiation and reflects visible light is disposed on a rear surface of a luminescent material plate, and light source lights in red, green and blue wavelength ranges are generated by shining ultraviolet light from a rear surface side of the luminescent material plate on to the luminescent material layers.
In addition, in Japanese Unexamined Patent Publication No. 2011-13320, the applicant of this patent application proposes a light source device that includes a laser oscillator as an excitation light source and a luminescent material plate of which a luminescent material layer is formed on a reflecting surface. In this proposal, a laser beam is shone on to the luminescent material layer from the laser oscillator, and luminescent light that is emitted from a luminescent material of the luminescent material layer is extracted from the same surface as the surface on to which the laser beam is shone on for use as light source light.
In a projector that uses a laser oscillator like the one described above, the laser beam that is emitted from the laser oscillator is coherent light in which phases are aligned, and therefore, it is necessary to prevent the laser beam from being emitted directly to the outside of the projector. Even in the case of the laser beam being prevented from leaking to the outside of the projector, when the laser beam is shone on to other positions than a predetermined position, there is caused a problem that a member lying in the position on to which the laser beam is shone is damaged.
Additionally, Japanese Unexamined Patent Publication No. 2003-295319 proposes a projector in which coherent light emitted from a laser oscillator is converted into incoherent light by a luminescent plate or a diffuse plate so that the incoherent light is emitted to the outside of the projector, whereby the laser beam is prevented from being emitted directly to the outside of the projector as light source light.
In this projector, a safety device is additionally provided to turn off the laser oscillator when the fall of the luminescent material or the diffuse plate is detected, or a diffuse plate is further disposed on the optical path of the incoherent light to enhance the safety of the projector. Namely, in these projectors, when the luminescent material or the diffuse plate falls, the safety device is activated to stop the emission of a laser beam from the laser oscillator momentarily so as to shorten the time during which the laser beam is shone on to other positions than the predetermined position within the projector or the laser beam leaks directly to the outside of the projector as short as possible, whereby the safety is ensured.
As has been described above, there is the projector in which light emitted from the excitation light source is shone on to the luminescent material layer and the luminescent light emitted from the luminescent material of the luminescent material layer is used as the light source light. In this projector, the quantity of luminescent light that is emitted from the luminescent material of the luminescent material layer can be increased by increasing the output of the excitation light source. However, in the case of the laser oscillator being used as the excitation light source, in the event that the power of the laser beam that is emitted from the laser oscillator is increased, there are fears that a brightness saturation is generated in the luminescent material or that a failure or damage is caused by burning. This results from time to time in complexity or difficulty in incorporating a detecting device or a detecting circuit for detecting the failure, damage or the like.